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Scirtothrips dorsalis
The chilli thrips1 or yellow tea thrips, Scirtothrips dorsalis Hood, is an extremely successful invasive species of pest-thrips1 which has expanded rapidly from Asia over the last twenty years, and is gradually achieving a global distribution. It has most recently been reported in St. Vincent (2004) Florida (2005), Texas (2006), and Puerto Rico (2007). It is a pest of economic significance with a broad host range, with prominent pest reports on crops including pepper, mango, citrus, strawberry, grapes, cotton, tea, peanuts, blueberry, and roses.2 Chilli thrips appear to feed preferentially on new growth, and infested plants usually develop characteristic wrinkled leaves, with distinctive brown scarring along the veins of leaves, the buds of flowers, and the calyx of fruit. Feeding damage can reduce the sale value of crops produced, and in sufficient numbers, kill plants already aggravated by environmental stress. This thrips has also been implicated in the transmission of three tospoviruses, but there is some controversy over its efficiency as a vector.3 This thrips has a rapid life cycle, and can develop from egg to adult in slightly less than two weeks under optimal weather conditions. Identification A tentative (but inconclusive) field identification can be made of this thrips by searching for the following traits under low power magnification: small size (under a millimeter in length), yellow coloration, dark antennae, and dark striping on the lower abdomen.456 It can be specifically identified and confirmed through the presence of forked sense cones on antennal segments III and IV, antennomeres I-II are pale and III to IX are dark; there are three discal setae on the lateral margins of abdominal tergites, with pronotal posteromarginal seta II nearly one and a half times the length of I or III, a complete posteromarginal comb on tergite VII; and three ocellar setae with III between posterior ocelli.478 Recent research concludes that S. dorsalis does represent a species complex of three or more disparate species who are morphologically similar but genetically distinct. Biology Like all thrips of suborder Terebrantia, S. dorsalis undergoes two nymphal stages followed by two "false" pupal stages,11 and under optimal conditions, this thrips may reach adulthood in approximately two weeks.12 However, research has shown that the length of these life-history stages are flexible within a group depending on an individual's access to nutrients13 and temperature.12 Nymphs entering the metamorphic process drop off of the plant during the first of two propual stages, and then complete their development in loose soil or leaf litter at the base of their host - but have been observed to pupate in any dark and humid crevice low on the plant, including bark and the folds of tightly packed lower leaves14 or flowers. The pupal process can range from two days to a full week.12 In temperate regions where the temperature falls below the critical lower threshold, non-diapausing adults are reported to overwinter in the soil or apical buds.151617 Colder temperatures may even drive pupation, but this has not been experimentally confirmed. Post-emergence, females have a pre-oviposition period of one to two days.12 Using their ovipositor, females lay single eggs within the plant tissue,18 and may lay an average of forty eggs during their lifetime.12 Females of S. dorsalis prefer to lay their eggs inside of young leaves and buds at the apical meristem of plants, but as populations increase, will lay their eggs within the surface of mature leaves.1119 Depending on temperature, eggs may gestate for one to three weeks.12 After hatching, larvae will migrate from older leaves to the newer growth at terminals.20 Like many thrips, S. dorsalis appears to prefer feeding on new growth and young plants,61115 and is often found on the newer top leaves on smaller plants, although individual plant morphology and chemistry may result in some distributional differences.15 Nymph populations will continue to increase so long as new shoots are allowed to grow,21 and adults are permitted to land.22 Physically manipulating the host by removing preferred feeding sites has been shown to reduce thrips density on the plant, but also to increase the relative rate of between-plot dispersal. History of Expansion Category:Thrips